Model Horse Reference -- Genetic Inheritance Basics

	Modification of Bay, Black & Chestnut
by C. Williams

All horses, under everything else, are either Bay, Black or Chestnut. The basic underlying color often has a lot to do with the final color you actually see, after other modifying loci are taken into account.

For this example, we're going to mix and match three loci together; A, E and C.

For this example, we're going to start with one parent, being Bay, and the other parent a Palomino.

Aa Ee CC

Bay Aa ee C^CrC

Palomino

Let's chart this up:

Bay X Palomino		Sire Aa Ee CC
Bay X Palomino		A E C	A E C	a E C	a E C	A e C	A e C	a e C	a e C
Dam Aa ee C^Cr	A e C	AA Ee CC Bay	AA Ee CC Bay	Aa Ee CC Bay	Aa Ee CC Bay	AA ee CC Chestnut	AA ee CC Chestnut	Aa ee CC Chestnut	Aa ee CC Chestnut
	A e C^Cr	AA Ee CC^Cr Buckskin	AA Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	AA ee CC^Cr Palomino	AA ee CC^Cr Palomino	Aa ee CC^Cr Palomino	Aa ee CC^Cr Palomino
	A e C	AA Ee CC Bay	AA Ee CC Bay	Aa Ee CC Bay	Aa Ee CC Bay	AA ee CC Chestnut	AA ee CC Chestnut	Aa ee CC Chestnut	Aa ee CC Chestnut
	A e C^Cr	AA Ee CC^Cr Buckskin	AA Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	AA ee CC^Cr Palomino	AA ee CC^Cr Palomino	Aa ee CC^Cr Palomino	Aa ee CC^Cr Palomino
	a e C	Aa Ee CC Bay	Aa Ee CC Bay	aa Ee CC Black	aa Ee CC Black	Aa ee CC Chestnut	Aa ee CC Chestnut	aa ee CC Chestnut	aa ee CC Chestnut
	a e C^Cr	Aa Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	aa Ee CC^Cr Smoky Black	aa Ee CC^Cr Smoky Black	Aa ee CC^Cr Palomino	Aa ee CC^Cr Palomino	aa ee CC^Cr Palomino	aa ee CC^Cr Palomino
	a e C	Aa Ee CC Bay	Aa Ee CC Bay	aa Ee CC Black	aa Ee CC Black	Aa ee CC Chestnut	Aa ee CC Chestnut	aa ee CC Chestnut	aa ee CC Chestnut
	a e C^Cr	Aa Ee CC^Cr Buckskin	Aa Ee CC^Cr Buckskin	aa Ee CC^Cr Smoky Black	aa Ee CC^Cr Smoky Black	Aa ee CC^Cr Palomino	Aa ee CC^Cr Palomino	aa ee CC^Cr Palomino	aa ee CC^Cr Palomino

Confusing? Sure... but you should notice a bit of a "pattern" to all of it. What is shown above shows all the possible allelic combinations between the genotypes of those particular two parents.

The numbers break down as such:

16 Chestnut (25%)
16 Palomino (25%)
12 Bay (18.75%)
12 Buckskin (18.75%)
4 Black (6.25%)
4 Smoky Black (6.25%)

However, if we remove the Cream gene effects... we have the following:

50% Chestnut Based colors
37.5% Bay Based colors
12.5% Black Based colors
You will notice that the % of Chestnut, Bay and Black colors overall, matches the same % as found in the example shown previously when the Cream locus was not involved. Likewise, 50% of this sample is affected by the Cream locus, as in the previous example regarding Cream color.

While it can be a bit of "busy work", it is possible to visibly chart out any number of loci in order to determine the % of probability to obtain any particular combination of alleles. However, for each pair of alleles you add in a chart, the number of columns and rows doubles:

2 alleles = 2x2 = 4 cells
4 alleles = 4x4 = 16 cells
6 alleles = 8x8 = 64 cells
8 alleles = 16x16 = 256 cells
10 alleles = 32x32 = 1024 cells

Just what you wanted, a math lesson too!

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